Wireless modems may send and receive data streams or data packets through an air interface. Wireless modems may be an analog type, such as a Bell 103 modem operating in accordance with the Bell 103 standard or other standards suitable for data communications over analog cellular voice channels. A wireless modem may be a digital type, operating in accordance with emerging standards suitable for data communications over digital cellular or PCS voice channels. Data transmissions may occur over wireless links by modulating a radio center frequency or band of frequencies in a prescribed fashion using one of a variety of modulation and encoding techniques, such as frequency modulation, frequency shift keying, phase shift modulation or frequency spreading methods, to accurately transmit and receive data through the airwaves. Once a radio communication channel is established, an incoming signal from a wireless modem may be received, amplified, demodulated and then reconstructed into data packets. An outgoing data packet may be formatted appropriately, and an outgoing transmission sent.
Transmissions of data between modems may occur over a wireless link, a wired link, a fiber link, or a combination thereof. An analog modem may operate, for example, using an analog mobile phone system such as the advanced mobile phone system (AMPS) over a band of frequencies nominally at 800 MHz. A digital modem may operate, for example, over a digital cellular or digital PCS (personal communication services) band nominally at 800 MHz, 900 MHz or 1900 MHz. An analog modem or a digital modem may operate, for example, over any suitable band of frequencies. Transmission of data over a digital wireless link using an analog modem may not work adequately due to circuitry and encoding algorithms in the mobile phone network that are optimized for voice transmissions. Data rates achievable with a digital wireless modem may be appreciably higher and more desirable than that of an analog wireless modem. Transmission of data from a digital or analog modem may occur, in part, over land-based communication lines, which may be part of a public switched telephone system.
The protocol required to transmit data streams or data packets between modems requires each modem to be operating in either an analog or digital mode. For a large number of phone calls coming into a call center, for example, it may be unknown whether an incoming data call is from an analog modem or a digital modem. Thus, the receiving end is required to determine whether an analog or a digital modem is initiating communication, and to set up the call accordingly.
A call may be initiated from a mobile vehicle, for example, to request and receive from a call center a variety of services, such as navigation instructions, directory assistance, road condition information, roadside assistance, Internet access, short messages, text messages, audio streams or video information. Many mobile vehicles are currently equipped with analog modems and switches that allow a sequence of data and voice sessions to occur. Newer vehicles may be equipped with digital modems, which offer higher speed and higher reliability in data transmissions. A call center may need, for example, to make a determination whether an incoming data call is being originated from a vehicle with an analog or a digital modem, and furthermore, to establish a connection with the mobile vehicle using the correct modem type such that the correct protocols may be used for accurate and reliable data transmission.
It is an object of this invention, therefore, to provide a method for modem protocol discrimination, and to overcome the deficiencies and obstacles described above.